1. Field of the Invention
This invention relates to a novel organic compound and a liquid crystal composition containing the same, and more particularly it relates to a biphenyl compound useful as a component of chiral smectic liquid crystal compositions useful for light switching elements by the use of ferroelectric liquid crystals.
2. Description of the Prior Art
Among liquid crystal display elements, those of the twisted nematic (TN) type display mode have currently been most widely used, but they are inferior in response rate to emissive type display elements (e.g. electroluminescence, plasma display, etc.), and various improvements in this respect have been attempted, but it appears, nevertheless, that the possibility of notable improvement has not been achieved. Thus, various liquid crystal display devices based on a different principle from that of TN type display elements have been tried in place thereof. Among these devices, there is a device of display mode utilizing ferroelectric liquid crystals (N. A. Clark et al, Applied Phys. lett., 36, 899 (1980)). This mode utilizes the chiral smectic C phase (hereinafter abbreviated to SC* phase), the chiral smectic H phase (hereinafter abbreviated to SH* phase) or the like of ferroelectric liquid crystals, and liquid crystal substances having such phases in the vicinity of room temperature have been desired as those suitable to this mode.
Now, ferroelectric display elements utilizing SC* phase have the following three superior specific features as compared with TN mode display elements.
The first specific feature is that the display elements reply at a very high rate so that the response time is 1/100 or less of those of conventional TN mode display elements. The second specific feature is that there is a memory effect so that the multiplex drive is easy in combination thereof with the above high rate response properties. The third specific feature is that when the gray scale is given in the case of TN display mode, this is effected by adjusting the impressed voltage, but there are raised difficult problems such as temperature dependency of threshold voltage, temperature dependency of response rate, etc.; whereas when the light-switching effect of SC* phase is applied, it is possible to readily obtain the gray scale by adjusting the reverse time of polarity and hence the display elements are very suitable to graphic display.
However, in spite of such superior specific features, the SC* phase region of currently known chiral smectic compositions is still insufficient particularly at its lower temperature part. Hence, in the aspect of practical use, too, liquid crystal substances covering the lower temperature region have been desired. Thus, the present inventors noted biphenyl compounds having a liquid crystal region at relatively low temperatures. However, most of the generally known biphenyl liquid crystal substances often have smectic phases as shown below other than SC phase and hence it has raised a problem to use such substances as a component for chiral smectic compositions (Demus. D et al, J. Phys. Coll. 36, 349 (1975)). ##STR2##
Thus, the present inventors have made extensive research on biphenyl compounds substituted by a halogen atom at the 3-position thereof, and as a result have found that the compounds exhibit superior specific features when they are used as a component for chiral smectic liquid crystal compositions.